High doses of pilocarpine are known to produce prolonged seizure activity in rats. Previous studies show that pretreatment with LiCl will sensitize rats to the convulsant effects of pilocarpine. Here we report that the anti-epileptogenic and anticonvulsant drug MK-801 (dizocilpine) paradoxically also sensitizes rats to pilocarpine induced limbic seizures and limbic status epilipticus (LSE). If rats were pretreated with MK-801, normally subconvulsive doses of pilocarpine rapidly produced LSE. LSE could be prevented by co-administration of either atropine or diazepam with MK-801...